Abstract

Tricaine methanesulfonate (MS-222) is a widely used aquatic immersion anesthetic that is considered to be safe and effective despite its significant impact on the pH of water. There are many proven benefits to buffering MS-222 prior to patient administration. In addition to increased anesthetic efficacy, buffering of MS-222 can prevent patients from developing metabolic acidosis, skin irritation, and eye damage.^1,2 In acidic environments, the anesthetic portion of MS-222 is positively charged, inhibiting its diffusion across the gills and increasing induction time.³

To neutralize the acidity of MS-222, and thus increase its efficacy and safety, current recommendations include buffering with sodium bicarbonate (NaHCO₃) at a ratio of 2 parts sodium bicarbonate:1 part MS-222, on a dry weight basis. This is only recommended if the alkalinity is less than 50 mg/liter as CaCO₃.² Many institutions buffer independent of the water’s alkalinity or salinity, and some recommendations call for a 4:1 NaHCO₃:MS-222 buffer.⁴ Other buffering agents used for medical procedures include sodium carbonate (Na₂CO₃) and hydroxide (OH^-). The short-term impacts of bicarbonate and carbonate on pH and alkalinity have been frequently evaluated but have not fully infiltrated into aquatic medicine practice.⁵ Sodium carbonate dissociation allows for the immediate binding of two hydrogen molecules, resulting in a faster effect on pH. In contrast, sodium bicarbonate dissociates into carbonate and hydrogen, creating an initial pH decrease and increase in alkalinity.^5,6

This study assessed the efficacy of this commonly used buffering method (2:1 NaHCO₃:MS-222), as well as the buffering ability of sodium bicarbonate and sodium carbonate, at varying concentrations for short term anesthetic procedures in teleosts and elasmobranchs. The three components evaluated included: 1) retrospective evaluation of pH changes observed in MS-222 anesthetic immersion baths buffered with 2:1 NaHCO₃:MS-222; 2) a pilot study evaluating various ratios of NaHCO₃:MS-222 to achieve complete buffering; and 3) a pilot study evaluating various ratios of Na₂CO₃:MS-222 to achieve complete buffering. Results indicate the pH changes with sodium bicarbonate buffering in a 2:1 ratio showed a 0.24–0.89 pH decrease. In marine systems, that range narrowed to 0.25–0.56 pH units. Within the confines of this study, sodium bicarbonate buffering demonstrated a relative inability to return the pH of MS-222 solution to its unadulterated pH. Buffering with increased ratios of sodium bicarbonate demonstrated a pH plateau within the examined window, after which, no increases in sodium bicarbonate demonstrated any effect on the sample pH. Sodium carbonate buffering demonstrated a superior ability to return the anesthetic solution to its initial pH. Although further statistical analysis of the data is pending, we recommend buffering marine systems with sodium carbonate at a ratio of 0.5:1 MS-222 on a dry weight basis to provide adequate buffering capacity.

Acknowledgements

The authors wish to thank The Florida Aquarium and its staff for their contributions to this study.

*Presenting author

Literature Cited

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2.  Noga, E. 2010. Methods for Treating Fish Diseases. In: Noga E editor. Fish Disease: Diagnosis and Treatment, 2nd ed., Wiley-Blackwell, p 375–420.

3.  Carter K, Woodley C, Brown R. 2010. A Review of Tricaine Methanesulfonate for Anesthesia of Fish. Reviews in Fish Biology and Fisheries, vol 2; 1:51–59.

4.  Mylniczenko N, Clauss T, Stamper A. 2014. Elasmobranchs and Holocephalans. In: West G, Heard D, Caulkett N editors. Zoo Animal and Wildlife Immobilization and Anesthesia, 2nd Edition, John Wiley & Sons, p 261–301.

5.  Pankow, James F. 1991. Aquatic Chemistry Concepts. CRC.

6.  Millero, Frank J. 1996. Chemical Oceanography. 2nd ed., Taylor & Francis.